Recognizing heretofore that objectionable variations of the proportioning ratio in a jet pump below the ratio of 1 to 5 is related to pressure variations of solute lift heights, the conventional practice, particularly with portable jet pumps, is to employ a single stage pump operating above the 1 to 5 ratio and reduce the significance of varying lift heights by developing a deep vacuum condition approaching zero p.s.i. absolute for the solute supply, and, then conducting the solute through a flow restriction to meter the amount of solute desired for the ratio proportioning.
Tolerated performance ratios available are generally limited to those above a 5 to 1 ratio in order to utilize the vacuum-solute-restriction arrangement. At greater proportioning ratios the efficiency is highly unstable with changes in solvent pressures, the ratio varying as the square root of the solvent pressure. With solute at approximately zero gauge pressures, ratios provided by a conventional single stage pump also present undesirable ratio variations with solvent pressure changes.